单项选择题

如图b)所示电源与图a)所示电路等效,则计算U S 和R 0 的正确算式为:

A.U S =U S +I S R 1 ,R 0 =R 1 ∥R 2 +R 3
B.U S =U S -I S R 1 ,R 0 =R 1 ∥R 2 +R 3
C.U S =U S -I S R 1 ,R 0 =R 1 +R 3
D.U S =U S +I S R 1 ,R 0 =R 1 +R 3